1. Field of the Invention
The present invention relates to a method for high speed rerouting in a multi protocol label switching network (MPLS), and in particular to a method for high speed rerouting in a MPLS switching network, which quickly deals with a failure in a node or a link comprising a multipoint-to-point label switched path (LSP) installed in Internet introducing the MPLS.
2. Description of the Related Art
Accompanying with tremendous popularity and traffic, Internet transfers real time traffic, priority traffic and an important business data, thereby rendering survivability of a communication network more important.
Among the related methods, a MPLS is characterized by setting a label switched path (hereinafter referred to as LSP) between terminals based on a routing information, and sticking a label of a specific length to a packet entered through an ingress label switching router (hereinafter referred to as LSR) according to its destination address and transferring the packet to the destination. Then, an intermediate LSR searches a label table from an input label of each packet and transfers the corresponding output level to the corresponding output link by swapping the corresponding output label with a new label.
As described above, the multi protocol label switching (hereinafter referred to as MPLS) method initially has been standardized for a main purpose of high speed transfer of the packet via the label swapping. However, the application of the method has been extended to a fast protection/recovery, a virtual private network, etc.
Among the applications of the MPLS method, a framework related to a MPLS path protection/recovery was suggested in “Framework for MPLS-based Recovery” by S. Makam, et al. dated July 2000.
As well known, the most important requirement in a recovery mechanism against various types of node or link failures generated in Internet is a fast setting of a substitute path and a fast routing of a traffic to the substitute path in order to minimize a packet loss. The fast rerouting path setting method for a point-to-point LSP in the MPLS network was suggested in “A Method for Setting an Alternative Label Switched Paths to Handle Fast Reroute” by D. Haskin and R. Krishnan dated May 2000. The main concept of the method is that when there generates a failure in a node or a link in the point to point LSP, a traffic transferred to a corresponding LSP is returned to a traffic source, which in turn transfers the traffic through an explicitly routed LSP (hereinafter referred to as ER-LSP) pre-set between the traffic source and a destination. Thus, the method has an advantage of minimizing the packet loss and high speed rerouting the traffic although the failure occurs in any point of the point-to-point LSP.
FIG. 1 is a diagram illustrating a process of protecting a point-to-point LSP in the fast rerouting path setting method in the MPLS network according to the conventional art.
First, an arrow marked with a thin line in FIG. 1 signifies a protected point-to-point LSP, an arrow marked with a thick line signifies a backup LSP, and an arrow marked with a dotted line signifies a traffic flow after a failure.
Referring to FIG. 1, when a failure occurs between a LSR5 and a LSR7, a traffic stream is loop-backed in the LSR5 to be sent to a source node (ingress LSR1) as marked with the dotted line, which in turn transfers the traffic stream to an ER-LSP (LSR1?LSR2?LSR4?LSR6?LSR7) set between a source LSR and a destination LSR, namely a LSR1 and a LSR7 so as not to overlap the protected LSP each other, thereby minimizing the packet loss and protecting the point-to-point LSP.
However, the point-to-point LSP protection method devised by Haskin has not suggested a process of protecting a multipoint-to-point LSP.
In other words, the LSR performs a label merging function, through which one multipoint-to-point LSP can be generated in most cases with respect to one FEC in the MPLS domain, with the exception of some cases including an ATM LSR, which does not support the merging.
Such point-to-point LSP protection method was suggested in “A Path Protectional/Restoration Mechanism for MPLS Networks” by C. Huang, et al. The method is characterized by transferring a fault indication signal (FIS) through a reverse tree of the LSP to notify the failure to a path switching LSR (PSL) of an upstream, if a failure occurs in a link or a node of the multipoint-to-point LSP. Here, the label merging LSR transfers the FIS in the upward direction. The PSL receiving the FIS transfers the corresponding traffic stream through the backup LSP to a path merging LSP (PML) in order to deal with a failure in a LSP of a downstream.
FIG. 2 is a diagram illustrating the multipoint-to-point LSP protection method suggested by C. Huang. An arrow marked with a thin line in FIG. 2 signifies the protected multipoint-to-point LSP between the PSL and the PML, and an arrow marked with a dotted line signifies the traffic flow after the FIS notification.
Referring to FIG. 2, when a failure occurs in a link between the LSR4 and the LSR6, the LSR4 senses the failure and transfers the FIS to the LSR3. The label merging LSR3 receiving the FIS transfers the FIS in the link between the LSR2 and the LSR9. Then, the final PSL (LSR1, LSR9) receiving the FIS switches the corresponding traffic stream to the backup LSP (LSR1?LSR5?LSR11?LSR6?LSR7,LSR9?LSR10?LSR7) to perform the multipoint-to-point LSP protection.
However, in the above process from sensing the failure to transferring the FIS up to the PSL, a volume of packet loss possibly occurs. In addition, if the PSL is not the ingress LSR, the LSP between the ingress LSR and the PSL cannot be protected.
Therefore, a more efficient mechanism for the multipoint-to-point LSP protection and recovery is under need.